/*
A* Algorithm Implementation using STL is
Copyright (C)2001-2005 Justin Heyes-Jones

Permission is given by the author to freely redistribute and 
include this code in any program as long as this credit is 
given where due.
 
  COVERED CODE IS PROVIDED UNDER THIS LICENSE ON AN "AS IS" BASIS, 
  WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED, 
  INCLUDING, WITHOUT LIMITATION, WARRANTIES THAT THE COVERED CODE 
  IS FREE OF DEFECTS, MERCHANTABLE, FIT FOR A PARTICULAR PURPOSE
  OR NON-INFRINGING. THE ENTIRE RISK AS TO THE QUALITY AND 
  PERFORMANCE OF THE COVERED CODE IS WITH YOU. SHOULD ANY COVERED 
  CODE PROVE DEFECTIVE IN ANY RESPECT, YOU (NOT THE INITIAL 
  DEVELOPER OR ANY OTHER CONTRIBUTOR) ASSUME THE COST OF ANY 
  NECESSARY SERVICING, REPAIR OR CORRECTION. THIS DISCLAIMER OF 
  WARRANTY CONSTITUTES AN ESSENTIAL PART OF THIS LICENSE. NO USE 
  OF ANY COVERED CODE IS AUTHORIZED HEREUNDER EXCEPT UNDER
  THIS DISCLAIMER.
 
  Use at your own risk!

*/

#pragma once
// used for text debugging
#include <iostream>
#include <stdio.h>
//#include <conio.h>
#include <assert.h>

// stl includes
#include <algorithm>
#include <set>
#include <vector>


// Fixed size memory allocator can be disabled to compare performance
// Uses std new and delete instead if you turn it off
#define USE_FSA_MEMORY 0

// disable warning that debugging information has lines that are truncated
// occurs in stl headers
#pragma warning( disable : 4786 )

namespace ECS
{

	// The AStar search class. UserState is the users state space type
	template <class UserState> class AStarSearch
	{

	public: // data

		enum
		{
			SEARCH_STATE_NOT_INITIALISED,
			SEARCH_STATE_SEARCHING,
			SEARCH_STATE_SUCCEEDED,
			SEARCH_STATE_FAILED,
			SEARCH_STATE_OUT_OF_MEMORY,
			SEARCH_STATE_INVALID
		};


		// A node represents a possible state in the search
		// The user provided state type is included inside this type

	public:

		class Node
		{
		public:

			Node *parent; // used during the search to record the parent of successor nodes
			Node *child; // used after the search for the application to view the search in reverse

			float g; // cost of this node + it's predecessors
			float h; // heuristic estimate of distance to goal
			float f; // sum of cumulative cost of predecessors and self and heuristic

			Node() :
			parent( 0 ),
				child( 0 ),
				g( 0.0f ),
				h( 0.0f ),
				f( 0.0f )
			{			
			}

			UserState m_UserState;
		};


		// For sorting the heap the STL needs compare function that lets us compare
		// the f value of two nodes

		class HeapCompare_f 
		{
		public:

			bool operator() ( const Node *x, const Node *y ) const
			{
				return x->f > y->f;
			}
		};


	public: // methods


		// constructor just initialises private data
		AStarSearch() :
			m_AllocateNodeCount(0),
#if USE_FSA_MEMORY
				m_FixedSizeAllocator( 1000 ),
#endif
				m_State( SEARCH_STATE_NOT_INITIALISED ),
				m_CurrentSolutionNode( NULL ),
				m_CancelRequest( false )
			{
			}

			AStarSearch( int MaxNodes ) :
			m_AllocateNodeCount(0),
#if USE_FSA_MEMORY
				m_FixedSizeAllocator( MaxNodes ),
#endif
				m_State( SEARCH_STATE_NOT_INITIALISED ),
				m_CurrentSolutionNode( NULL ),
				m_CancelRequest( false )
			{
			}

			// call at any time to cancel the search and free up all the memory
			void CancelSearch()
			{
				m_CancelRequest = true;
			}

			// Set Start and goal states
			void SetStartAndGoalStates( UserState &Start, UserState &Goal )
			{
				m_CancelRequest = false;

				m_Start = AllocateNode();
				m_Goal = AllocateNode();

				assert((m_Start != NULL && m_Goal != NULL));

				m_Start->m_UserState = Start;
				m_Goal->m_UserState = Goal;

				m_State = SEARCH_STATE_SEARCHING;

				// Initialise the AStar specific parts of the Start Node
				// The user only needs fill out the state information

				m_Start->g = 0; 
				m_Start->h = m_Start->m_UserState.GoalDistanceEstimate( m_Goal->m_UserState );
				m_Start->f = m_Start->g + m_Start->h;
				m_Start->parent = 0;

				// Push the start node on the Open list

				m_OpenList.push_back( m_Start ); // heap now unsorted

				// Sort back element into heap
				push_heap( m_OpenList.begin(), m_OpenList.end(), HeapCompare_f() );

				// Initialise counter for search steps
				m_Steps = 0;
			}

			// Advances search one step 
			unsigned int SearchStep()
			{
				// Firstly break if the user has not initialised the search
				assert( (m_State > SEARCH_STATE_NOT_INITIALISED) &&
					(m_State < SEARCH_STATE_INVALID) );

				// Next I want it to be safe to do a searchstep once the search has succeeded...
				if( (m_State == SEARCH_STATE_SUCCEEDED) ||
					(m_State == SEARCH_STATE_FAILED) 
					)
				{
					return m_State; 
				}

				// Failure is defined as emptying the open list as there is nothing left to 
				// search...
				// New: Allow user abort
				if( m_OpenList.empty() || m_CancelRequest )
				{
					FreeAllNodes();
					m_State = SEARCH_STATE_FAILED;
					return m_State;
				}

				// Incremement step count
				m_Steps ++;

				// Pop the best node (the one with the lowest f) 
				Node *n = m_OpenList.front(); // get pointer to the node
				pop_heap( m_OpenList.begin(), m_OpenList.end(), HeapCompare_f() );
				m_OpenList.pop_back();

				// Check for the goal, once we pop that we're done
				if( n->m_UserState.IsGoal( m_Goal->m_UserState ) )
				{
					// The user is going to use the Goal Node he passed in 
					// so copy the parent pointer of n 
					m_Goal->parent = n->parent;

					// A special case is that the goal was passed in as the start state
					// so handle that here
					if( false == n->m_UserState.IsSameState( m_Start->m_UserState ) )
					{
						FreeNode( n );

						// set the child pointers in each node (except Goal which has no child)
						Node *nodeChild = m_Goal;
						Node *nodeParent = m_Goal->parent;

						do 
						{
							nodeParent->child = nodeChild;

							nodeChild = nodeParent;
							nodeParent = nodeParent->parent;

						} 
						while( nodeChild != m_Start ); // Start is always the first node by definition

					}

					// delete nodes that aren't needed for the solution
					FreeUnusedNodes();

					m_State = SEARCH_STATE_SUCCEEDED;

					return m_State;
				}
				else // not goal
				{

					// We now need to generate the successors of this node
					// The user helps us to do this, and we keep the new nodes in
					// m_Successors ...

					m_Successors.clear(); // empty vector of successor nodes to n

					// User provides this functions and uses AddSuccessor to add each successor of
					// node 'n' to m_Successors
					bool ret = n->m_UserState.GetSuccessors( this, n->parent ? &n->parent->m_UserState : NULL ); 

					if( !ret )
					{

						typename std::vector< Node * >::iterator successor;

						// free the nodes that may previously have been added 
						for( successor = m_Successors.begin(); successor != m_Successors.end(); successor ++ )
						{
							FreeNode( (*successor) );
						}

						m_Successors.clear(); // empty vector of successor nodes to n

						// free up everything else we allocated
						FreeAllNodes();

						m_State = SEARCH_STATE_OUT_OF_MEMORY;
						return m_State;
					}

					// Now handle each successor to the current node ...
					for( typename std::vector< Node * >::iterator successor = m_Successors.begin(); successor != m_Successors.end(); successor ++ )
					{

						// 	The g value for this successor ...
						float newg = n->g + n->m_UserState.GetCost( (*successor)->m_UserState );

						// Now we need to find whether the node is on the open or closed lists
						// If it is but the node that is already on them is better (lower g)
						// then we can forget about this successor

						// First linear search of open list to find node

						typename std::vector< Node * >::iterator openlist_result;

						for( openlist_result = m_OpenList.begin(); openlist_result != m_OpenList.end(); openlist_result ++ )
						{
							if( (*openlist_result)->m_UserState.IsSameState( (*successor)->m_UserState ) )
							{
								break;					
							}
						}

						if( openlist_result != m_OpenList.end() )
						{

							// we found this state on open

							if( (*openlist_result)->g <= newg )
							{
								FreeNode( (*successor) );

								// the one on Open is cheaper than this one
								continue;
							}
						}

						typename std::vector< Node * >::iterator closedlist_result;

						for( closedlist_result = m_ClosedList.begin(); closedlist_result != m_ClosedList.end(); closedlist_result ++ )
						{
							if( (*closedlist_result)->m_UserState.IsSameState( (*successor)->m_UserState ) )
							{
								break;					
							}
						}

						if( closedlist_result != m_ClosedList.end() )
						{

							// we found this state on closed

							if( (*closedlist_result)->g <= newg )
							{
								// the one on Closed is cheaper than this one
								FreeNode( (*successor) );

								continue;
							}
						}

						// This node is the best node so far with this particular state
						// so lets keep it and set up its AStar specific data ...

						(*successor)->parent = n;
						(*successor)->g = newg;
						(*successor)->h = (*successor)->m_UserState.GoalDistanceEstimate( m_Goal->m_UserState );
						(*successor)->f = (*successor)->g + (*successor)->h;

						// Remove successor from closed if it was on it

						if( closedlist_result != m_ClosedList.end() )
						{
							// remove it from Closed
							FreeNode(  (*closedlist_result) ); 
							m_ClosedList.erase( closedlist_result );

							// Fix thanks to ...
							// Greg Douglas <gregdouglasmail@gmail.com>
							// who noticed that this code path was incorrect
							// Here we have found a new state which is already CLOSED
							// anus

						}

						// Update old version of this node
						if( openlist_result != m_OpenList.end() )
						{	   

							FreeNode( (*openlist_result) ); 
							m_OpenList.erase( openlist_result );

							// re-make the heap 
							// make_heap rather than sort_heap is an essential bug fix
							// thanks to Mike Ryynanen for pointing this out and then explaining
							// it in detail. sort_heap called on an invalid heap does not work
							make_heap( m_OpenList.begin(), m_OpenList.end(), HeapCompare_f() );

						}

						// heap now unsorted
						m_OpenList.push_back( (*successor) );

						// sort back element into heap
						push_heap( m_OpenList.begin(), m_OpenList.end(), HeapCompare_f() );

					}

					// push n onto Closed, as we have expanded it now

					m_ClosedList.push_back( n );

				} // end else (not goal so expand)

				return m_State; // Succeeded bool is false at this point. 

			}

			// User calls this to add a successor to a list of successors
			// when expanding the search frontier
			bool AddSuccessor( UserState &State )
			{
				Node *node = AllocateNode();

				if( node )
				{
					node->m_UserState = State;

					m_Successors.push_back( node );

					return true;
				}

				return false;
			}

			// Free the solution nodes
			// This is done to clean up all used Node memory when you are done with the
			// search
			void FreeSolutionNodes()
			{
				Node *n = m_Start;

				if( m_Start->child )
				{
					do
					{
						Node *del = n;
						n = n->child;
						FreeNode( del );

						del = NULL;

					} while( n != m_Goal );

					FreeNode( n ); // Delete the goal

				}
				else
				{
					// if the start node is the solution we need to just delete the start and goal
					// nodes
					FreeNode( m_Start );
					FreeNode( m_Goal );
				}

			}

			// Functions for traversing the solution

			// Get start node
			UserState *GetSolutionStart()
			{
				m_CurrentSolutionNode = m_Start;
				if( m_Start )
				{
					return &m_Start->m_UserState;
				}
				else
				{
					return NULL;
				}
			}

			// Get next node
			UserState *GetSolutionNext()
			{
				if( m_CurrentSolutionNode )
				{
					if( m_CurrentSolutionNode->child )
					{

						Node *child = m_CurrentSolutionNode->child;

						m_CurrentSolutionNode = m_CurrentSolutionNode->child;

						return &child->m_UserState;
					}
				}

				return NULL;
			}

			// Get end node
			UserState *GetSolutionEnd()
			{
				m_CurrentSolutionNode = m_Goal;
				if( m_Goal )
				{
					return &m_Goal->m_UserState;
				}
				else
				{
					return NULL;
				}
			}

			// Step solution iterator backwards
			UserState *GetSolutionPrev()
			{
				if( m_CurrentSolutionNode )
				{
					if( m_CurrentSolutionNode->parent )
					{

						Node *parent = m_CurrentSolutionNode->parent;

						m_CurrentSolutionNode = m_CurrentSolutionNode->parent;

						return &parent->m_UserState;
					}
				}

				return NULL;
			}

			// For educational use and debugging it is useful to be able to view
			// the open and closed list at each step, here are two functions to allow that.

			UserState *GetOpenListStart()
			{
				float f,g,h;
				return GetOpenListStart( f,g,h );
			}

			UserState *GetOpenListStart( float &f, float &g, float &h )
			{
				iterDbgOpen = m_OpenList.begin();
				if( iterDbgOpen != m_OpenList.end() )
				{
					f = (*iterDbgOpen)->f;
					g = (*iterDbgOpen)->g;
					h = (*iterDbgOpen)->h;
					return &(*iterDbgOpen)->m_UserState;
				}

				return NULL;
			}

			UserState *GetOpenListNext()
			{
				float f,g,h;
				return GetOpenListNext( f,g,h );
			}

			UserState *GetOpenListNext( float &f, float &g, float &h )
			{
				iterDbgOpen++;
				if( iterDbgOpen != m_OpenList.end() )
				{
					f = (*iterDbgOpen)->f;
					g = (*iterDbgOpen)->g;
					h = (*iterDbgOpen)->h;
					return &(*iterDbgOpen)->m_UserState;
				}

				return NULL;
			}

			UserState *GetClosedListStart()
			{
				float f,g,h;
				return GetClosedListStart( f,g,h );
			}

			UserState *GetClosedListStart( float &f, float &g, float &h )
			{
				iterDbgClosed = m_ClosedList.begin();
				if( iterDbgClosed != m_ClosedList.end() )
				{
					f = (*iterDbgClosed)->f;
					g = (*iterDbgClosed)->g;
					h = (*iterDbgClosed)->h;

					return &(*iterDbgClosed)->m_UserState;
				}

				return NULL;
			}

			UserState *GetClosedListNext()
			{
				float f,g,h;
				return GetClosedListNext( f,g,h );
			}

			UserState *GetClosedListNext( float &f, float &g, float &h )
			{
				iterDbgClosed++;
				if( iterDbgClosed != m_ClosedList.end() )
				{
					f = (*iterDbgClosed)->f;
					g = (*iterDbgClosed)->g;
					h = (*iterDbgClosed)->h;

					return &(*iterDbgClosed)->m_UserState;
				}

				return NULL;
			}

			// Get the number of steps

			int GetStepCount() { return m_Steps; }

			void EnsureMemoryFreed()
			{
#if USE_FSA_MEMORY
				assert(m_AllocateNodeCount == 0);
#endif

			}

	private: // methods

		// This is called when a search fails or is cancelled to free all used
		// memory 
		void FreeAllNodes()
		{
			// iterate open list and delete all nodes
			typename std::vector< Node * >::iterator iterOpen = m_OpenList.begin();

			while( iterOpen != m_OpenList.end() )
			{
				Node *n = (*iterOpen);
				FreeNode( n );

				iterOpen ++;
			}

			m_OpenList.clear();

			// iterate closed list and delete unused nodes
			typename std::vector< Node * >::iterator iterClosed;

			for( iterClosed = m_ClosedList.begin(); iterClosed != m_ClosedList.end(); iterClosed ++ )
			{
				Node *n = (*iterClosed);
				FreeNode( n );
			}

			m_ClosedList.clear();

			// delete the goal

			FreeNode(m_Goal);
		}


		// This call is made by the search class when the search ends. A lot of nodes may be
		// created that are still present when the search ends. They will be deleted by this 
		// routine once the search ends
		void FreeUnusedNodes()
		{
			// iterate open list and delete unused nodes
			typename std::vector< Node * >::iterator iterOpen = m_OpenList.begin();

			while( iterOpen != m_OpenList.end() )
			{
				Node *n = (*iterOpen);

				if( !n->child )
				{
					FreeNode( n );

					n = NULL;
				}

				iterOpen ++;
			}

			m_OpenList.clear();

			// iterate closed list and delete unused nodes
			typename std::vector< Node * >::iterator iterClosed;

			for( iterClosed = m_ClosedList.begin(); iterClosed != m_ClosedList.end(); iterClosed ++ )
			{
				Node *n = (*iterClosed);

				if( !n->child )
				{
					FreeNode( n );
					n = NULL;

				}
			}

			m_ClosedList.clear();

		}

		// Node memory management
		Node *AllocateNode()
		{

#if !USE_FSA_MEMORY
			Node *p = new Node;
			return p;
#else
			Node *address = m_FixedSizeAllocator.alloc();

			if( !address )
			{
				return NULL;
			}
			m_AllocateNodeCount ++;
			Node *p = new (address) Node;
			return p;
#endif
		}

		void FreeNode( Node *node )
		{

			m_AllocateNodeCount --;

#if !USE_FSA_MEMORY
			delete node;
#else
			m_FixedSizeAllocator.free( node );
#endif
		}

	private: // data

		// Heap (simple vector but used as a heap, cf. Steve Rabin's game gems article)
		std::vector< Node *> m_OpenList;

		// Closed list is a vector.
		std::vector< Node * > m_ClosedList; 

		// Successors is a vector filled out by the user each type successors to a node
		// are generated
		std::vector< Node * > m_Successors;

		// State
		unsigned int m_State;

		// Counts steps
		int m_Steps;

		// Start and goal state pointers
		Node *m_Start;
		Node *m_Goal;

		Node *m_CurrentSolutionNode;

#if USE_FSA_MEMORY
		// Memory
		FixedSizeAllocator<Node> m_FixedSizeAllocator;
#endif

		//Debug : need to keep these two iterators around
		// for the user Dbg functions
		typename std::vector< Node * >::iterator iterDbgOpen;
		typename std::vector< Node * >::iterator iterDbgClosed;

		// debugging : count memory allocation and free's
		int m_AllocateNodeCount;

		bool m_CancelRequest;

	};
}

   